This paper presents some theoretical and experimental analyses of the rotating-magnet based mechanical antenna (RMBMA), a promising portable transmitting antenna for ELF-ULF (3-3000 Hz) wireless communication. Based on the Amperian current model, a theoretical model is developed to analyze the electromagnetic fields generated by RMBMA. A prototype is manufactured and measured, and the measurements coincide well with the calculations based on the established theoretical model. The results reveal that this new technique can create a constant channel condition in complex propagation environment, and an RMBMA with a small size can produce an AC magnetic field of 1 pT at hundreds of meters across lossy media, such as soil and sea water.

A novel broadband ±45° dual-polarized magneto-electric (ME) dipole antenna is proposed for 2G/3G/LTE/5G (3.3-3.6 GHz)/WiMAX applications. The proposed antenna has Γ-shaped feeding strips to impart a wide impedance bandwidth for its special structure. Stable antenna gain and radiation pattern are realized by using a rectangular box-shaped reflector instead of planar one. The antenna is fabricated and measured. The measured results show that a common impedance bandwidth is 83% with standing-wave ratio (SWR) ≤ 1.5 from 1.59 to 3.83 GHz and port-to-port isolation larger than 25 dB within the bandwidth. The measured antenna gains vary from 8 to 10.8 dBi and from 8 to 10.6 dBi for port 1 and port 2, respectively. The antenna has nearly symmetrical radiation patterns with low back lobe radiation both in horizontal and vertical planes, and broadside radiation patterns with narrow beam can also be obtained. The proposed antenna can be used for multiband base stations in next generation communication systems.

This paper presents a dual-band Multi-Input Multi-Output (MIMO) antenna design with acceptable isolation and compact size for wireless applications. The proposed antenna operates at two frequencies (2.75 GHz-5.3 GHz) and consists of two symmetrical monopoles with a T-shaped junction that is added on the upper layer of the substrate and used to connect the two monopoles and the ground plane. The T-shaped junction is added to enhance the isolation between the two antennas. Different forms of slots have been etched on the ground plane to adapt the frequency bands to the desired frequencies. The simulations and measurement are used to examine the performance of the antenna in terms of S parameters, radiation patterns and the envelope of correlation coefficient. The results show that the MIMO antenna has two resonance frequencies (2.75 GHz and 5.3 GHz), is suitable for WLAN applications and comes with a mutual coupling that is less than 12 dB. As a result, an envelope correlation coefficient lower than 0.001 and a diversity gain higher than 9.98 dB are obtained, which means that the antenna has a remarkable diversity gain at operating bands.

In this paper, design and development of a novel electromagnetics band gap cell is presented. The EBG cell is designed aiming its use at relatively low frequencies. It is designed as a uni-planar structure to simplify the fabrication processes. It consists of multiple parallel combinations of L and C. These components are realized using planar microwave integrated circuit technology. The components L & C are designed as a meander-line inductor and inter-digital capacitors, respectively. The cell is perfectly symmetrical along x and y-axes to have uniform performance along two orthogonal directions. It is evaluated for its S-parameters and reflection phase. Simulated and measured results are presented for frequency range of 0.885 GHz to 3.1 GHz.

In this article, a negative index metamaterial (NIM) superstrate is designed and cooperated with the filtenna to produce miniaturize communication front end for gain enhancement without any substantial increase in the profile of the whole structure. A finite array Double H Split Ring (DHSR) of 11x9 unit cells has been designed on a dielectric substrate to form the NIM metamaterial superstrate. The proposed superstrates and filtenna have an overall dimension of 0.67λ_ox0.54λ_ox1.19λ_o at 10.16 GHz with 10.6 dB total broadside gain in simulation and 9.8 dB in measurement at 10.22 GHz (λ_o = 30 mm). This miniaturized communication front end which consists of a filter, an antenna and a gain enhancer affords smaller size with the overall volume of 0.43λ_o³ in the context of using metamaterial superstrate for gain enhancement reported in the earlier literatures.

This paper proposes a composite right/left-handed cylindrical waveguide. Negative permeability is realized by the cutoff TM₀₁-mode in a hollow waveguide, and negative permittivity is realized by the cutoff dominant TE-mode in a sector waveguide with a ridge. Usefulness of the proposed cylindrical waveguide is verified from the numerical computations of both the dispersion diagrams and the transmission characteristics of the structure with finite-number unit cells. Finally, measurement of the fabricated waveguides is performed for the experimental verification.

A simple broadband and wide stopband half-mode substrate integrated waveguide (HMSIW) filter is proposed. Symmetrical complementary split ring resonators (CSRRs) and metallized holes are loaded on the surface of the HMSIW resonator. Metallized holes placed in the center of the CSRRs are used to create two passbands. CSRRs can reduce the return loss of the first passband, and a transmission zero is introduced to suppress the performance of the second passband, thus generating broadband covering the entire X-band. The simulated results show that the center frequency and fractional bandwidth of the filter are 9.26 GHz and 60.7%. There is a transmission zero at 13.18 GHz, and the insertion loss in the range of 12.30 to 21.46 GHz is better than -10 dB, which means that the out-of-band suppression performance is good. The measured results are in good agreement with the simulated ones. This new combination not only obtains broadband frequency, but also makes the filter more compact. The filter has some practical and application significance.

In this paper, a novel multi-physics parametric modeling approach using artificial neural networks (ANNs) for microwave passive components is proposed. In the proposed approach, the ANN is used to learn the nonlinear relationships between electromagnetic (EM) behaviors and multi-physics design variables. The trained model can accurately represent the EM responses of the passive components with respect to the multi-physics input parameters. Therefore, the proposed model can provide accurate and fast prediction of EM responses using low computational cost and little time for multi-physics design. The advantage of the proposed model is demonstrated by two microwave examples: the proposed model can save about 98% computational cost compared with the EM model, and the CPU time of the proposed model is less than 0.1 s while that of the EM model needs many minutes.

In this paper, we propose a simulation model of electromagnetic waves propagation in media with different kinds of dispersions. This model exploits the dependence of the polarization current density and the voltage electric in the context of the Transmission Line Matrix method with the Symmetrical Condensed Node (SCN-TLM) and novel voltage sources. By solving Maxwell's and polarization current density equations, the proposed model, named JE-TLM, gives a full solution of Maxwell's equations and polarization terms which describe the Lorentz linear dispersion, nonlinear instantaneous Kerr and retarded Raman effects. The scattering matrix characterizing the SCN with the new voltage sources is provided, and the numerical results are compared with those of the literature or with the theoretical ones.

Study on the interactions between electromagnetic fields and biological tissue at high frequency band is an important aspect in the area of wireless communications. The use of millimeterwave frequency band for fifth Generation (5G) devises involves new challenges in terms of Radio Frequency Electromagnetic Field Exposure (RF-EMF) limits and compliance assessment since the basic restrictions for limiting human exposure change from the Specific Absorption Rate (SAR) to the power density. The Electromagnetic Field Exposure to the human head has been studied based on power density by means of numerical simulation for the frequency band of 10 GHz. Study on radio frequency energy absorption has been done based on radiation from a printed monopole antenna at frequency of 10 GHz, transmitting directly towards the human head tissue model. Human head model is constructed from magnetic resonance images with frequency dependent tissue electrical properties. It is shown that at millimeter wave frequency, i.e. 10 GHz, with realistic source (20 mW) and head-source separation distance (10 mm), the amount of power density is in the range of regulatory limits and requirements on EMF exposure. The obtained results might provide valuable information for the design of 5G handheld devices and EMF compliance assessment.

A novel array-antenna decoupling surface (ADS) for mutual coupling reduction in microstrip patch antenna is proposed in this paper. The proposed ADS is composed of a group of primary reflector patches and a pair of rectangular and T-shaped secondary reflector patches. Through generating the reflected waves with equal magnitude but out of phase of the coupling waves, the isolation of the antenna elements could be significantly improved by the novel proposed ADS. Then, for verification, a two-element microstrip antenna array covered by the proposed ADS with an edge-to-edge separation of 0.11λ₀ (λ₀ is the wavelength of the operating frequency in free space) was designed and fabricated. As expected, the experimental results have demonstrated that an additional 40.4 dB isolation enhancement at the resonant frequency was achieved by the proposed ADS. Moreover, a much wider bandwidth of the isolation was also obtained than that of return loss of 10 dB. In addition, a gain improvement of 0.95 dB was achieved at 2.45 GHz by utilizing the novel ADS. Thus, the decoupling structure can be applied to multiple-input multiple-output (MIMO) systems for its simple structure and high isolation providing.

Surface impedance of thin graphite films with metallic properties is evaluated by a waveguide technique based on measuring reflection and transmission coefficients of thin film membranes at operating frequencies in rectangular waveguides. One- and two-layer membranes of finite thickness, completely filling the waveguide cross-section, are investigated. Formulas allowing analytical estimates of surface impedances for nonmagnetic films made of amorphous carbon are derived. Simulation results for graphite films at frequencies from 5 to 10 GHz are analyzed.

In this paper, the correlation coefficients of skewed dipole arrays for antenna diversity are analyzed theoretically for each polarization characteristic and in various propagation environments. The correlation is not simply increased by two closely located antennas with different polarization characteristics and it is not decreased by increased antenna distance. This result is interpreted from the correlation analysis of two skewed dipoles with different polarization characteristics. The embedded beam patterns of the two skewed dipoles are calculated using the mutual impedances derived using the effective length vector (ELV) method; then, the mutually coupled correlation coefficients for θ, ϕ, and total polarizations are effectively derived. The correlations are also analyzed for various realistic propagation environments using statistical channel models with angular density functions and cross polarization discriminations (XPDs). Finally, this paper provides an effective correlation analysis for two dipoles and proposes optimal geometries for the two skewed dipoles in various propagation environments for each polarization characteristic and with environmental variables.

This letter presents an omnidirectional printed dipole antenna array with a wide bandwidth. The array is composed of four dipole units etched on a thin substrate, which is simple in structure and easy to be processed. By modifying the triangle-shaped radiation dipole units and gradually increasing the width of microstrip feeding transmission line, the performance of the dipole antenna array is greatly improved. Simulation results show that this omnidirectional antenna has a peak gain greater than 7.39 dBi, and the impedance bandwidth is 16% (VSWR<1.6), ranging from 2.3 to 2.7 GHz.

This paper proves that the use of conventional diagnostic methods of rotor crack and local demagnetization based on the harmonic analysis of the output voltage or counter-electromotive force is effective only with a certain ratio of the number of slots and poles. This statement was proved experimentally. The diagnostic method of the rotor cracks and local demagnetization which is universal for all types of windings and the number of slots of 2-pole synchronous electric machines with permanent magnets is proposed. The mathematical apparatus for the implementation of the proposed method is developed and verified with the help of FEM and experimental studies. All the experimental studies have been carried out for various rotor magnetic systems and a different number of stator slots.

In this paper, we are interested in the design of a new Ultra-Wideband (UWB) directional Vivaldi antenna with narrow beam, in the frequency range of 1.17 to 4.75 GHz. The simulation of the designed antenna is carried out on Computer Simulation Technology Microwave Studio (CST-MWS). The mutual coupling effect reduction is considered. The designed antenna is tested for Ground Penetrating Radar (GPR) and Through the Wall applications. The emitted waveform is a Stepped Frequency Continuous Wave (SFCW) signal, generated by a Vector Network Analyser (VNA). The acquired raw data are focused by using back projection algorithm.

A dual-port reader antenna based on magnetic coupling in near-field (NF) and linear polarization in far-field (FF) is proposed for UHF RFID multiservice applications. The prototype consists of four straight dipoles fed by double-side parallel stripline structure with two feed ports. The proposed antenna can operate at different modes by feeding each corresponding port. In NF mode, a strong and uniform magnetic field can be generated over the interrogation zone. In FF mode, a linearly polarized performance can be obtained. The antenna prototype is printed onto a piece of FR4 substrate with an overall size of 180 × 180 × 1.6 mm³. The measured tests on reading range are carried out, and the results exhibit 100% reading rate for near-field tags within 100 mm and reading distance of far-field tags is 120 cm. Both simulated and measured results show good capability for near- and far-field applications.

In this paper, a novel stabilization scheme to prevent parametric oscillations in power amplifiers is presented. Based on a new oscillation detection approach, the inductive degeneration technique was used, for the first time, to successfully stabilize a high-power amplifier and prevent parametric oscillations. A 0.15 um AlGaN/GaN Microwave Monolithic Integrated Circuit high power amplifier operating at 5.8 GHz with 10% fractional bandwidth was designed and successfully stabilized using this approach. The proposed (4.7 x 3.7) mm² three-stage amplifier achieves a saturated output power of 35 W with 29% power added efficiency and a large-signal gain of 26 dB.

Four wave mixing (FWM) in optical fiber is unwanted effect to an optical transmission system, which can severely limit the wavelength division multiplexing (WDM) and lower the transmission efficiency. In this work, the robustness of normal Non-Return-to-Zero (NRZ), Return-to-Zero (RZ) and Modified-Duobinary-Return-Zero modulation (MDRZ) to FWM have been evaluated. Furthermore, the system performance is evaluated with the effect of fiber length tuning and applying 160 Gb/s data rate. The findings show that the RZ modulation offers a lower FWM power of -44 dBm at 700 km fiber length than -30 and -38 dBm of NRZ and MDRZ respectively at the same fiber length. In terms of system performance at the first channel and 700 km distance, the minimum BER is observed in normal RZ modulation, equal to 1.2×10^-23. It is also noticeable that if NRZ and MDRZ modulations are applied, the system performance will be quickly changed and get worse, where the BEARs are increased to 1.3×10^-6 and 1.3×10^-8 consecutively at same channel and parameters.

A dual-polarized broadband single-layer reflectarray antenna based on square spiral element is presented in this paper. Two designs with similar square spiral structures but different construction processes and transition patterns are investigated and compared. The comparison results show that the design utilizing the sweeping method of varying the length of the first stub of one-arm square spiral is more suitable for the building the reflectarray. Several 441-element reflectarray antennas fed by horn with different offset angles are also simulated and compared to show the broadband characteristic. A reflectarray with offset angle of 15 degrees is then fabricated and tested. The measured results show good radiation performances, and the 1-dB gain bandwidth of 34.7% is obtained. The measured gain is 27.1 dB at the center frequency of 15 GHz, which is equivalent to 45.6% aperture effifficiency.